Geology of Bering Land Bridge National Preserve
Learn more about the geology of Bering Land Bridge National Preserve.
Overview
The Bering Land Bridge National Preserve (BLBNP) covers 2.7 million acres of land on the Seward Peninsula coastline of Northwest Alaska. It is located 55 miles east of Russia and 100 miles north of Nome. The preserve was established in December 1980 by the Alaska National Interest Lands Conservation Act (ANILCA), and protects a section of land remaining from the prehistoric “land bridge” known as Beringia that once connected Asia with North America more than 12,000 years ago (The Bering Land Bridge Theory, 2021). It came into existence due to a lower sea level during the Last Glacial Maximum [during] of the Pleistocene Ice Age. Sea level subsequently rose as ice sheets covering North America melted. Alaska and Russia are now separated from each other by the Bering strait, a narrow passage connecting the Bering Sea and the Arctic Ocean. The preserve is primarily tundra, a flat area of land with few trees and permafrost (permanently frozen subsoil) that is common in arctic regions. The park is extremely remote and can be reached only by helicopter, boat, snow machine, or on foot as there are no roads. The preserve has great variation in topography, ranging from mountains to volcanic fields, rolling tundra, and shallow volcanic depressions called maars. Almost the entirety of the preserve is underlain by permafrost, causing the formation of features such as pingos, and thermokarst lakes. Pingos are hills formed by ice upheaval beneath the soil and can stand up to 90m in height. A thermokarst lake is also called a thaw lake or tundra lake, which is a depression developed by thawing permafrost.
The focus of much fascination within the park centers on the pre-historic land bridge connection across the Bering Strait, connecting Russia and Alaska and allowing migration of humans, birds, wildlife, and the spread of plant species from Asia to North America. The Bering Land Bridge is today the submerged Bering-Chukchi shelf, a portion of continental crust underlying Alaska and Siberia (Lanik et al., 2019).
Geologic History - Cenozoic: 66 million years ago - present
During this time the Ice age ended and volcanic eruptions of the Seward Peninsula began, creating volcanic formations such as flows and lava cones. The Alaska Range also underwent significant uplift and mountain-building related to subduction of Pacific ocean crust beneath south-central and southwestern Alaska during the Cenozoic; geologic features related to this subduction may extend to the Seward Peninsula. There are five Cenozoic volcanic units in the preserve, including the Kugruk, Imuruk, and Gosling volcanics, as well as the Camille and Lost Jim lava flows (Lanik et al., 2019).
During the Pleistocene (late Cenozoic), much of the earth's water was frozen in glaciers and ice sheets as thick as 4km, dropping sea level as much as 300 feet across the globe and exposing the Bering land bridge around 20,000 years ago (About-Beringia (NPS), 2021; Nature and Science, 2021). Time periods in which vast amounts of water are trapped in ice sheets and the mean global temperature drops, are referred to as a glacial periods. The land bridge was exposed during a time referred to as the Last Glacial Maximum, the time during the most recent glacial period when the ice sheets were at their largest mass. During glacial intervals when sea levels were low, the Bering Land Bridge could become much drier and relatively ice-free in lowlands compared to the rest of Canada and western Siberia (Elias, 2015).
Devil Mountain, Maars, & the Espenberg Volcanic Field
Devil mountain is one of three basaltic shield volcanoes from the Quaternary period located in the Espenberg Volcanic field in the BLBNP. Shield volcanoes are formed of successive lava flows with a profile resembling a shield. Lava erupting from these kinds of volcanoes is much thinner and less viscous than some other types of volcanoes, meaning it has a higher capacity to flow than thicker lavas.
Surrounding Devil mountain are cinder cones, which form above volcanic vents on the main volcano as pyroclastic fragments or cinders build up the characteristic cone shape. Devil Mountain is estimated to be one of the youngest volcanic formations in the preserve.
The Espenberg Volcanic Field also contains maarsꟷ volcanic craters formed from large explosions that eventually fill to become a lake. These explosions can be due to either volcanism or hot volcanic material coming into contact with groundwater (called phreatomagmatic explosions) (Bizarre Maars (NPS), 2021). Beringia is the most northern point in the world where maars lakes have been recorded (Other Maar Lakes (NPS), 2021). Those on the Seward Peninsula are the largest in size and longest in lake sediment archives in Alaska (Discovery of paleoclimate proxies (NPS), 2021). The individual maars containing lakes have been named (from west to east) White Fish maar, Devil Mountain maar, South Killeak maar, and the North Killeak maar.
Within the sediment archives of these maar lakes were found a class of organic molecule called alkenones, which are stable, can be preserved for long periods of time, and degrade slowly. They are produced by special algae within the lake and can be used to reconstruct past spring temperatures for paleoclimate research (Discovery of paleoclimate proxies (NPS), 2021).
Credit: National Park Service
Imuruk Lake & Volcanic Field
Imuruk lake is 8 miles long and located in the Imuruk volcanic field, the other primary volcanic field in the preserve. This field contains as many as 75 volcanic vents and lava flows of varying age across the plateau formed by the volcanic rock (Imuruk Volcanic Field (NPS), 2021). The lost Jim lava flow contains volcanic features called pahoehoe flows, which are fluid basaltic composition flows that cool in a folding pattern. The Camille volcanic flows are pahoehoe flows from the Camille volcano that are about 10,000-20,000 years old. About 800,000-900,000 years ago, the Gosling volcanic flows issued from large lava domes containing calderasꟷ a volcanic crater caused by the collapse of a volcano. These domes erupted up to 20 times during a 100,000-year timespan until flow stopped and caused the collapse of the calderas (Volcanoes and Lava flows (NPS), 2021). These flows can be as thick as 300 ft. The Kugruk volcanic field encompasses the oldest and primarily buried volcanic flows, dating at 26-28 million years old and reaching 40 feet in thickness. They are the most weathered flows, indicating a warmer climate during or shortly after formation compared to present day (Volcanoes and Lava flows (NPS), 2021).
The eruption of the Lost Jim lava flow in particular is important to the Kawerak native peoples of the area and is described in their oral history as being witnessed by one of their legendary leaders, named Ekeuhnick. Such oral histories are recorded in three native languages still spoken in the Beringia region: Iñupiaq, Siberian and Central Yupik. A majority of Siberian Yupik peoples are located on the Russian side of the Bering Strait.
Geologic History- Mesozoic: 251.9 - 66 million years ago
During this time a mountain forming period called the Brookian Orogeny, the Canadian Basin opened, there was emplacement of granitic plutons in the preserve, and the tectonic plate on which the preserve is located rotated to its current position (Lanik et al., 2019).
The Brookian Orogeny took place around 170-145 million years ago, following collision of the southern Brooks Range and Seward Peninsula with the Angayucham oceanic arc (Moore et al., 1994; Miller et al, 2017). The granitic plutons on the preserve formed after the Brookian Orogeny, but prior to the Cenozoic (Lanik et al., 2019.
Granite Tors
The granite tors within the preserve are essentially freestanding granite spires formed as surface granite was worn away. Many of the tors are part of the Oonatut Granite Complex, which is composed of medium- to coarse-grained biotite granite, estimated to be 69-80 million years old by radiometric dating (Geology of Serpentine Hot Springs (NPS), 2021).
Geologic History- Paleozoic: 541 million years ago - 251.9 million years ago
This period included volcanism and plutonic emplacement in the Seward Peninsula and southern Brooks Range areas. The Eastern Brooks Range was a part of Laurentia continental terrane during this time while the Western Brooks Range; Siberia and the Seward Peninsula were a part of Baltica continental terrane (Miller et al., 2017, and references therein).
Serpentine Hot Springs
The Serpentine Hot Spring and the Arctic hot springs are located in an area of the preserve named Hot springs Creek. Both springs have almost identical temperatures and chemical compositions. The heat in the springs is not a result of volcanism but is associated with the plutons of the Oonatut Granite Complex (Geology of Serpentine Hot Springs (NPS), 2021). A vast majority of thermal springs in the preserve occur within 3 miles (laterally) of one of these plutons. Deep circulation of water through fractures in the granitic plutons at depths of 2-3 miles causes it to absorb heat before returning to the surface at the hot springs (Geology of Serpentine Hot Springs (NPS), 2021). While the heat has been correlated to the granitic plutons, the age of the plutons has not been correlated with the age of the springs; the springs formed significantly later than the plutons were emplaced.